The purpose of the work described in this proposal is to continue study of the mechanisms of cellular immmunity and hypersensitivity. Our aim is to acquire knowledge of basic mechanisms which can be used to rationally manipulate these cellular processes in certain human clinical conditions where enhancement of cellular immunity might lead to prevention or alleviation of disease such as infections or neoplasia, or where suppression might diminish tissue injury caused by cellular hypersensitivity. The proposed investigation is a direct outgrowth of our interests in the interaction of lymphocytes, their mediators and macrophages in cellular immunity and of recent observations on the effects of lymphocytes and their products on macrophage activation as it relates to bactericidal and bacteriostatic function. The specific aims of this proposal include the following: a. Further study of the lymphocyte-macrophage interaction in resistance to infection. b. Analysis of normal vs activated macrophages. c. Investigation of the recognition of tumor cells by activated macrophages. d. Further purification of migration inhibitory factor. e. Isolation of macrophage membranes. f. Studies on the mechanism of action of human transfer factor.